At an environmental science workshop this past spring, Columbia University ecologist Shahid Naeem mused, "Gone are the good old days when you could do ecology just because it was fun." Those in his profession might once have analyzed ecosystems purely for the intellectual challenge, but today their work has an urgency to it. They return to a forest they had worked in, only to find it chopped down; they hear older colleagues reminisce about birds last seen decades ago; they walk on permafrost turned mushy by global warming.

As described in this special issue, the world is now under-going a remarkable set of transitions: population growth has reached an inflection point and is starting to level off, the developing world is becoming developed, and environmental problems that used to be local-ized are radiating everywhere. The interconnected changes are, in demographer Joseph Chamie's words, a "quiet revo-lution" that reaches into every corner of life. They pose threats but also offer opportunities. Having seen firsthand what is happening, the authors of the articles here have thrown themselves into the task of helping society navigate the shoals ahead.

Some people don't like that. They say that the social and environmental sciences already smack of politics and that scientists should steer clear of anything resembling advocacy. These critics claim to be standing up for "real science," yet they define science in a way that most practicing scientists find alien. True, there comes a point when scientists offering advice on political issues act in the capacity of private citizens rather than researchers--and when that happens, they should represent themselves as such. And they do run a risk of letting ideology backwash into their technical judgment. Yet the extreme alternative--disengagement--is not an option. It would be a denial of everything scientists do, an abdication of the responsibility that comes with knowledge.

Scientific American would not even exist without the desire of scientists to reach beyond the confines of their laboratories and help to make the world a better place. Articles on social and environmental sciences, including ones with strong points of view, have filled our pages since the magazine's founding in 1845. On many past occasions--notably in 1974, 1980 and 1989--we have devoted an entire issue to the challenges of balancing economic development with environmental protection.

Some critics, though, are unconcerned with philosophical debates about what scientists should or shouldn't do. Their complaints boil down to: I don't agree with what you're saying, and rather than engage with it, I will deny your legitimacy to say it. Sadly, that has become the dominant rhetorical strategy in the country today--one that will only make it that much harder to address the challenges of the coming decades.

Geographer Jared Diamond's recent book Collapse documents past civilizations that could not recognize or bring themselves to change unsustainable ways. Largely because of science, our civilization has the chance not only to avoid their fate but to enter an age of unprecedented prosperity. Science is not and should not be the sole factor in decision making; others, such as moral values, are also crucial. But we need to go into these decisions with our eyes open to what is going on in the world.